1. Field of the Invention
The present disclosure relates to modulators and modulation methods, and more specifically to modulators and modulation methods using a dual-port memory.
2. Description of the Related Art
A Gaussian Minimum Shift Keying (GMSK) modulation adopts a Gaussian filter and is widely used in mobile communication systems, such as Global System for Mobile Communications (GSM), Bluetooth, Mobile LAN, and the like. GMSK modulation adopts the Gaussian filter, thereby having low side lobes compared with those of Quadrature Phase Shift Keying (QPSK) modulation and Minimum Shift Keying (MSK) modulation.
GMSK modulation adopts a look-up table to generate a GMSK waveform signal corresponding to a digital input bit stream instead of performing complicated calculations to generate the GMSK waveform signal, so that high-speed GMSK modulation may be obtained. The look-up table respectively stores data corresponding to an in-phase GMSK waveform signal and data corresponding to a quadrature phase GMSK waveform signal.
U.S. Pat. No. 5,255,288 discloses a GMSK modulator that has a first read-only memory (ROM) look-up table and a second ROM look-up table respectively storing in-phase waveform data and quadrature phase waveform data. According to the U.S. Pat. No. 5,255,288, the number of word lines is reduced from 1,024 to 256 so as to reduce a size of the ROMs.
U.S. Pat. No. 5,954,787 discloses a GMSK modulator in which the look-up table stores data corresponding to a ¼ period of a periodic waveform signal and stores only one of sine function values and cosine function values, so that the capacity of memory needed for the look-up table can be decreased.
United States Patent Application Publication No. 2004/0179630 discloses a GMSK modulator that uses a mapping logic and has a look-up table of which a size corresponds to a half of a size of data corresponding to a GMSK waveform signal, so that the capacity of memory needed for the look-up table can be decreased.
As described above, various methods for decreasing the capacity of memory needed for the look-up table have been developed.